The present invention generally relates to a method and an apparatus for forming a resin composite part, and more particularly to an improved method and apparatus for forming a resin a composite part utilizing a mold surface for mitigating post-cure machining of the resin composite part.
The use of composite material in commercial and military applications is well known. Composite materials are desirable due to their mechanical characteristics such as a high strength to weight ratio and high thermal tolerances. As such, composite materials are frequently used to build structural supports, such as ducts for aircrafts.
Because of their high strength coupled with light weight, composite parts are being increasingly utilized as structural components in a variety of articles. Typical composite part material includes glass or graphite fibers that are embedded in resins such as epoxy, phenolic or bismaleimide resins. Generally, the fiber and resin are xe2x80x9claid-upxe2x80x9d over a mold and then cured under elevated temperature, and pressure. Composite parts destined to be used in the aerospace or aircraft industries must meet exacting requirements as to their structural integrity. To meet these exacting requirements, precise control of temperature and pressure conditions is required during their cure.
A widely utilized system for forming structure composite parts uses what are termed xe2x80x9cprepregs.xe2x80x9d These are sheets of fiber that have uncured resin embedded therein. The prepreg is laid over the mold and while being maintained in position against the mold, it is subjected to heat and pressure to cure the prepreg into the composite material. Various apparatus are known to maintain the prepreg in contact with the mold during heat and pressure treatment such as press platens, vacuum bags or trapped rubber molding systems.
However, prepregs are expensive, its shelf life is limited, and it must normally be kept refrigerated until used. In addition, special handling safety procedures are necessary when handling uncured resin impregnated fibers.
This has led to the use of processes that do not require such xe2x80x9cprepregs.xe2x80x9d These processes are similar in that fibers are still laid-up in a mold, however it is initially resin free. The lay-up is subsequently vacuum bagged, and a vacuum is drawn from between the bag and mold such that the lay-up is compressed by atmospheric against the mold. However, in this process, resin is simultaneously drawn in through an inlet port in the vacuum bag and through the lay-up impregnating it. Finally the now impregnated fibers are heated until the resin is cured.
As shown in FIGS. 1 and 2, regardless of using processes that include prepregs or not, one factor remains the same. The final cured product, namely, cured resin composite part, needs to be trimmed. More specifically, whether the process involves prepregs, or not, the resin composite part resulting therefrom has to be trimmed to the desired engineering specifications.
Such trimming of the resin composite part frequently occurs at the end of its manufacturing process. In particular, the resin composite part is formed first before meeting its dimensional specifications, in which such specifications are only met thereafter to achieve its practical applicability. In the industry that utilizes such step, the trimming is typically done by expensive machines, thereby becoming an inevitable obstacle to cost-saving and efficient manufacturing.
The resin composite part is often subjected to 5-axis machining to meet the engineering specifications desired by manufacturers. More specifically, 5-axis machining is utilized not only for trimming, but for drilling as well. As indicated in the immediate paragraph above, such machines to carry out the functions of 5-axis machining are expensive, simultaneously being essential components in the overall manufacturing of resin composite parts.
Moreover, the materials employed to form the resin composite part are costly as well. In the industry where such resin composite parts are often mass-produced, any material that is trimmed or machined from each cured product may prove to be significant when added together. In view of today""s manufacturing process for forming resin composite parts, the excess materials resulting therefrom may be inescapable, ultimately having to be exposed to post-cure machining such as 5-axis machining.
Thus, there has long been a need in the industry, and in the aerospace industry in particular for a method and an apparatus for forming a resin composite part utilizing a mold surface in order to mitigate post-cure machining of the resin composite part. In particular, there is a need to manufacture resin composite parts without performing post-cure machining of excess materials resulting therefrom in order to achieve cost-saving and efficient manufacturing thereof.
In accordance with the present invention, there is provided a method of forming a resin composite part utilizing a mold surface for mitigating post-cure machining of the resin composite part. The method provides for forming a resin preform having a peripheral geometry similarly sized and configured as a configuration of the mold surface. The mold surface is sized and configured to receive the resin preform. The resin preform is then cured to form a resin composite part with the resin composite part being conformed to the configuration of the mold surface for mitigating post-cure machining of the resin composite part.
More specifically, the resin preform may be formed by cutting the preform. A template may be utilized to cut the resin preform. Such preform may be fabricated from a fiber material. Subsequent to forming the resin preform, the method may further comprise the step of selectively applying at least one ply on the resin preform such that none of the at least one ply extends beyond peripheral edges thereof. More specifically, the at least one ply may be cut such that none of the at least one ply extends beyond the peripheral edges of the preform and laid on the resin preform.
In one embodiment, the mold surface defines a recess therein and further has a mold line adjacent the recess. The recess has edges adapted to engage the resin preform therein up to the mold line, in which the edges may have a height equal to, or greater than, a thickness of the resin composite part. The edges may be non-stick edges selected from the group consisting of low expansion metals, invar, aluminum, graphite, Teflon, butyl rubber plus Teflon film and cured silicone rubber. In addition, the resin preform has an end portion, wherein the method further comprises the step of positioning the resin preform on the mold surface. Specifically, the preform end portion is extendable up to the mold line and simultaneously engages the recess.
In accordance with an embodiment of the method of the present invention, subsequent to forming the resin preform, a peel ply is laid over the resin preform. The peel ply is extendable up to the mold line. Furthermore, the mold surface defines an excess trim adjacent to the mold line, and the method further comprises the steps of laying first and second films over the peel ply, the first and second films extending to the excess trim, and positioning a dam between the first and second films adjacent to the mold line.
In addition, subsequent to forming the resin preform a flexible covering having an end may be placed over the preform and the mold surface. The end of the flexible covering is sealed to the mold surface. The flexible covering may be a vacuum bag having a vacuum attachment. Moreover, subsequent to forming the resin preform, resin may be distributed onto the resin preform.
In another embodiment, the mold surface has at least one tooling pin adapted to form at least one drilling hole on the resin composite part. The tooling pin is further adapted to form at least one countersinking hole on the resin composite part.
Further, the mold surface may be a Bond Jig. The mold surface ay be a hat mold surface having mold lines, defining a pyramidal configuration therebetween. The hat mold surface further has recesses between the pyramidal configuration and the mold lines. The resin preform having end portions is cut within 3 degrees of normal to the pyramidal configuration in intermediate area thereof, wherein the preform end portions extend up to the mold lines and simultaneously engage the recesses.
In another embodiment, the mold surface may be a generally planar mold surface, wherein the planar mold surface has a frame surrounding peripheral edges thereof. In addition, the preform may also be a generally planar preform having four sides extendable up to the frames.
Further the step of curing the resin preform may include autoclaving the resin preform to form the resin composite part. In addition, subsequent to the step of curing or autoclaving the resin composite part having edges nay have process capability (Cp) greater or lower than 1.33. When the process capability (Cp) is lower than 1.33, the method further comprises the step of sanding the edges of the resin composite part to conform to the configuration of the mold surface.
The present invention addresses and overcomes the above-described deficiency of prior art prepreg and, non-prepreg processes and a apparatus by providing a method that utilizes the mold surface to mitigate post-cures machining of the cured resin composite part. More specifically, the mold surface is sized and configured to engage a netted resin preform in its defined recess up to its mold line, thereby already configured to the configuration of the mold surface before cure. In this respect, not only does the present invention mitigate the need to use expensive post-cure machining, such as 5-axis machining for example, but it also minimizes the excess materials formed after cure.